Spoilage Organisms in Fresh Meat
During the slaughtering process of cattle and poultry some species of micro-organisms are able to develop and colonise under certain conditions. The growth develops when specific type / amount of essential nutrients are available mainly on the surface of the meat products. Population of the survived micro-organisms is directly dependent on the type and properties of the meat, atmosphere, storage and the processing approaches.
Gram negative aerobic rods and coccobacilli bacteria are the main contributory factors to the spoilage of chilled fresh meat. During the chilling of fresh meat, aerobic species of micro-organisms including Pseudomonas, Acinetobacters, Psychrobacter and Moraxella exhibit the quickest growth. Some other micro-organisms like Shewanella and Enterobacteriaceae have less substantial effect on developing spoilage of meat as they require certain conditions for their metabolism and growth.
During the post mortem changes, glycogen is degraded by muscle fibers as a result of aerobic and anaerobic activity to achieve the required ATP for cellular structure and osmotic balance. The ratio of compounds with low-molecular weight characteristic will dramatically modify due to the physical change of muscle to meat. The composition of post-mortem meat is considered as an analytical factor at the initial stage of the chilling storage. At this stage there are protein and lipid-based nutrients in addition to water availability. The glucose content of beef is normally between 0.1 to 0.5% which is utilised by micro-organisms present on the surface of meat. This will postpone the consumption of other nutrients including amino acids. If glucose concentration is not sufficiently supplied for microbes, meat spoilage can occur as the bacteria will attack amino acids due to the less availability of glucose.[Copyright note: http://www.labreports.info] This can result in increasing ammonia and PH of the meat.
Insufficient content of glucose may be in consequence of improper treating of cattle. This can lead to reducing glycogen proportion in live animals. Organoleptically speaking, meat from frightened and / or starved animals is known as DFD (Dark, Firm, Dry) meat. The spoilage can be postponed by the addition of glucose to DFD meat as it can be consumed by bacteria; therefore amino acids remain intact.
In comparison to the Gram negative bacteria, the Gram positive bacteria are highly tolerant to inhibiting conditions (pH, decreased water availability, less oxygen, heat treatment and curing). Fresh meat can largely provide essential growth factors for Lactic acid bacteria (LAB) including Lactobacillus (rod shape) and Enterococcus Leuconostoc (cocci). Rich source of glucose, glycogen, glucose 6-phosphate in addition to amino acids and vitamins in meat can easily encourage the growth of “fastidious” LAB.
Psychrotrophic Gram positive contaminants on fresh lamb carcass mostly consist of Caseobacter polymorphus, Corynebacterium, Kurthia, Brevibacterium, Cellulomonas and Listeria. Results from the laboratory experiments have confirmed that substantial presence of genera Staphylococci and Micrococci during the processing meat in abattoirs. These organisms are classified as primary Gram positive contaminants and they have the same microscopic appearance and are mostly present on the skin of animals and human. Genera Micrococci are not anaerobically able to produce acid from glucose metabolism while Staphylococci can anaerobically synthetise acid (mainly from glycerol).
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